PSI - Issue 24

Giovanni Meneghetti et al. / Procedia Structural Integrity 24 (2019) 190–203 Meneghetti et al./ Structural Integrity Procedia 00 (2019) 000–000

193

4

Steel plates, having same initial dimensions, were prepared from commercial hot rolled plates and then reduced to 10 mm thickness by milling. All plates were grinded, brushed and properly clamped by means of tack welded fixture bracket in order to minimize welding distortions. Final specimen’s dimensions were obtained by cutting after welding. All welding operations were done by ‘Istituto Italiano della Saldatura’ (IIS). ADI 1050 showed ultimate strength R m =1100 MPa, yield strength R p02 =920 MPa, Brinell hardness HBW=350÷380 and elongation at fracture A 5 =8%; all mechanical properties were obtained from specimens cut from the plates. S355J2 mechanical properties according to EN10025-2 are ultimate strength R m min =470 MPa, yield strength R p02 min =355 MPa, HBW=160÷180 and elongation at fracture A 5 min =22%. 3.1 Production of specimens Welding parameters were tuned (Meneghetti et al. (2019)) by considering the specimen’s thickness of 10 mm, weld bead dimensions, misalignments, runs number and all the different types of dissimilar joint investigated. The main issue was to prevent martensite formation and cracks nucleation within HAZ of ADI 1050: the proper set of welding parameters was identified in such a way that the resulting hardness was as close as possible to the base ADI material. However, the formation of ledeburite layer close to the weld metal cannot be avoided as in this area ductile iron always undergoes metastable solidification after re-melting. The complete set of welding parameters is reported in Table 1. In particular, pulsed arc fully mechanized GMAW-welding process was adopted. Table 2 summarizes the specimens’ geometry and preparation. Macrographic/micrographic tests as well as VT, PT and HBW test were carried out on all specimens. Quality level for imperfections was according to ISO 5817-B.

Table 1. GMAW welding parameters adopted for specimens Mode of metal transfer Welding position Torche angle direction Filler material

Current& Polarity [A]

Voltage [V]

Travel speed [mm/min]

Heat input [kJ/mm]

S C NiFe-2 EN ISO 1071 ø 1.2 mm

UNI EN ISO 6947 PA

CCPI 120÷130

P

15° forehand

24÷25

220÷340

0.41÷0.71

Preheat temperature

EN 13916-TC 200°C

Interpass temperature

EN 13916-TC 250°C

Shielding

ISO 14175 M21 (Ar-CO 2 80-20), flow rate 16÷18 lt/min

4. Specimen characterisation For all specimens, micro-hardness and residual stress profiles, along with misalignments, were measured (Meneghetti et al. (2019)) in order to evaluate the conditions of post-weld materials in ADI-steel joints. However, for the sake of brevity, only hardness measurements are reported in the present contribution. Vickers hardness HV0.5 profiles were measured in order to recognize microstructural alterations. The results are reported in Figs. 2-5 and confirm that heat affected zone of ADI 1050 mainly consists in graphite nodules in pearlitic matrix and ledeburite layer close to weld metal; HAZ of S355J2 consists in ferritic-pearlitic matrix.